cabbie - 9:33 am on Jun 12, 2012 (gmt 0)
I have had no problems thus far swapping adsense codes on sites.I run my sister's code off and on some of my sites to boost her income.
Sometimes, I have hers and my adsense codes on the one page with no ill effect.
In fact, just recently, I took adsense from a website that belonged to me and I gave it to another sister of mine who had a interest in developing it and she applied for an adsense account with it immediately and was accepted with it.
I don't access either of their accounts though.